Mystery continues to shroud Big Ben's injury. Mike Tomlin appeared at his weekly news conference yesterday dressed casually. He should have worn blue scrubs or a white smock because he was asked to play doctor instead of Steelers coach. Or, he might have pulled out a magnifying glass because he turned into a private eye halfway through it. The subject was quarterback Ben Roethlisberger and his sore right shoulder. That's what Tomlin called it last week and what he called it again yesterday, even though NBC-TV Sunday night made a big deal about Roethlisberger having a separated right shoulder. The Post-Gazette confirmed Monday that indeed Roethlisberger has a low-grade separated shoulder, or, more technically, a slight injury to the AC joint, a Type 1 shoulder separation. There are six types of shoulder separations, and the more serious can require surgery. But, basically, Roethlisberger's injury is how Tomlin described it, a sore shoulder. Technically, though, NBC-TV was correct in calling it a separation.